It is now well established that maternal malnutrition will retard fetal growth. It has been assumed that the primary cause of this growth retardation is a reduction in nutrient supply. Since maternal malnurition affects placental growth and metabolism it is possible that placental function, as manifested by the ability to transfer nutrients, is also impaired. Recent data have demonstrated that maternal malnutrition in the rat is associated with a reduced rate of transfer of glucose and alpha-amino isobutyric acid (AIB) from the maternal circulation into the fetus. Although indirect evidence suggests that this reduced transfer of nutrients was due to altered placental transfer the exact mechanism of the effect has not been established yet. Studies are therefore being proposed in order to measure placental transport of nutrients in vitro and in vivo in normal and malnourished animals. The in vitro studies will be done in the guinea pig. It is hoped that using this approach we will be able to increase our understanding of the effects of malnutrition on placental transport systems.